Code-based, electromagnetic-field-responsive graphic data-acquisition system

ABSTRACT

An electromagnetic-field-responsive (preferably optical), code-based, graphic data-acquisition system for tracking the operational status of a mobile write-effective component (stylus, eraser, etc.) in relation to a defined writing-surface area. The preferred embodiment features an active optical structure which is disposed adjacent the writing-surface area for creating, by scanning, a defined zone of optical radiation, optically reactive, retroreflective code structure which is joined to the mobile component and which is capable of reacting (reflecting the same) to radiation within the zone when the code structure intersects the zone, a reaction monitoring structure for monitoring the reaction behavior of the code structure and for producing a related response, and interpretation structure which acquires that response and determines therefrom the desired operational-status-tracking information. Modification to this preferred structure are also illustrated and discussed.

This application is a continuation of U.S. applications Ser. No.08/148,837 entitled MARKING SYSTEM WITH PEN-UP/PEN-DOWN TRACKING SYSTEMnow U.S. Pat. No. 5,434,370, Ser. No. 08/147,997 entitled CALIBRATION OFGRAPHIC DATA-ACQUISITION TRACKING SYSTEM now abandoned, Ser. No.08/148,660 entitled OPTICAL-SCANNING SYSTEM EMPLOYING LASER AND LASERSAFETY CONTROL and Ser. No. 08/148,691 entitled GRAPHIC DATA-ACQUISITIONSYSTEM UTILIZING LIGHT-SOURCE STRUCTURE WITH EXTRANEOUS-LIGHT FILTERING,all filed on Nov. 5, 1993, all of which are incorporated by referenceinto this application.

TECHNICAL FIELD

This invention relates to a code-based, electromagnetic-field-responsive(and preferably optically responsive), one-to-one, graphicdata-acquisition system for tracking, in relation to a definedwriting-surface area, the operational status (position, character,inclination etc.) of a mobile, write-effective component, such as awriting stylus (pen, marker) or eraser, in the system.

BACKGROUND AND SUMMARY OF THE INVENTION

Early notions of digitizing the activities at what might be thought ofas an "electronic blackboard" date at least to the mid-1960s, at whichtime emphasis was placed on the communication of graphical data,specifically handwriting and sketches, from one location to another.U.S. Pat. No. 3,706,850 discloses a system related to such activity.

At about the same time, interest was strong afoot in digitizing theactivity on a tabletop - - - for example for the entry of line drawingsinto a computer. Systems involving this interest are collectively knownas graphic tablets, and U.S. Pat. No. 3,838,212 is an early example ofdevelopment matters in this area.

By the mid-1980s, a third kind of a product group developed to addressthe need for creating a local hard copy of material written and sketchedonto a dry-erase, so-called whiteboard. This generic group of systems,known collectively as electronic copyboards (ECBs), relatesfundamentally to stand-alone devices that have much in common with wellknown reducing photocopiers.

Each of these devices attempts, in its own right so-to-speak, to providethe user with a natural communication metaphor - - - with familiarwriting tools. In the cases of the electronic blackboard and theelectronic copyboard, the metaphor is a wall-mounted surface meant formass viewing, with marking or writing accomplished by colored markers,and erasing occurring by wiping with an eraser. In the case of thegraphic tablet, the metaphor is a desktop slate and stylus meant forindividual use.

Those skilled in the art recognize that both electronic blackboards andelectronic copyboards typically require special surfaces and arerelatively expensive. Further, they do not readily support the use ofcolor presentations, and the typical electronic copyboard cannotcommunicate real-time transitional information - - - i.e. it mustbatch-transmit (like a facsimile) an entire sheet, or page, ofinformation at a time.

Other systems and approaches generally in this line of technical art areillustrated, for example, in U.S. Pat. Nos. 4,558,313, 4,777,329 and5,023,408. The '313 patent focuses on an indicator-to-data processinginterface which employs a light source and a background reflector asconstituents in a system to monitor occlusion of light occurring fromthe positioning and movement of a manually moved indicator over asurface. The '329 patent, which is based upon on my own prior line ofdevelopment in this field, addresses attention to a graphic input systemwhich employs ultrasound to monitor the position of a mobile elementover a surface. The '408 patent describes an electronic blackboardincluding a sensing tablet which senses the position of a "writing tool"that includes a tuned circuit having a predetermined resonant frequency.

All of these various approaches in the prior art in this area offer, intheir own respective ways, operational advantages in certainapplications, but nevertheless also have some common, as well asdifferentiated, deficiencies which are correctively addressed by thesystem of the present invention. For example, prior art systems of thetype outlined above are relatively complicated and costly (asmentioned). They are not necessarily readily retrofittable, for example,to a wide variety of writing-surface structures which are already inhundreds of thousands of users' possessions. Further, prior art systemsare not particularly adapted to yield information about the condition ofa writing stylus or an eraser (write-effective component) much beyondits position or station over a writing surface. Many systems, as alreadyindicated, cannot communicate changing, real-time positioning of such acomponent. Nor are known prior art systems adapted to handle moresophisticated informational issues, such as (1) differentiatedwriting-line widths which may result from differentiated angulation of awriting stylus, or (2) parallax under similar circumstances, or (3) thewidth of an eraser swath under circumstances where an eraser'sconfiguration is such that it has different effective erasure-widthsfrom different angular points of view.

Accordingly, and in the setting just described, a general object of thepresent invention is to provide a novel graphic data-acquisition systemwhich offers not only the various features and advantages made availableby prior art, generically-related systems, but which also addresseseffectively the various performance, cost, simplicity andsophistication, etc., issues just briefly mentioned.

Proposed by the present invention, with these considerations in mind, isa code-based electromagnetic-field-responsive, and preferably optically(or near optically) responsive, one-to-one, graphic data-acquisitionsystem which employs active transceiver structure (a pair or morepreferably), including a scanning light-beam source and alight-reflection (or light-retroreflection) monitoring structure (1) tocreate a zone of scanned or swept radiation extending closely over adefined writing-surface area, and (2) to monitor reflections (orretroreflections) of such radiation from such an area, all incooperation with a passive write-effective component, such as a writingstylus (pen, marker) or eraser, which is equipped with code structure,such as a bar code structure, that reflects (retroreflects), orotherwise interacts responsively to, radiation created (by scanning)over the writing-surface area. As mentioned, the system of the inventionpreferably operates in the optical, or near-optical, portion of theelectromagnetic spectrum. Thus, in the preferred embodiment of theinvention described herein, two transceiver structures are employed atspaced stations, with each such structure including a light source inthe form of a laser operating generally in the optical, or perhaps moreprecisely in the near-optical, portion of the electromagnetic spectrum,and specifically, at a preferred wavelength of 780-nanometers. Thesystem is referred to as a one-to-one system since communication takesplace directly between a transceiver structure and a write-effectivecomponent moved over the writing-surface area.

By employing passive, radiation-responsive code structure on a componentthat moves over a writing surface to create or remove images, the systemachieves remarkable simplicity. Further, by utilizing a code structureassociated with such a component, a great deal of information, quitebeyond simply that relating to the position of the component relative tothe writing-surface area, can be acquired. For example, one candistinguish immediately whether the component is a writing implement oran erasing implement, can determine the nature or character of writtenline width or eraser swath, can detect, for example, specific color inthe instance of a colored writing instrument being used, and also withrespect to a writing instrument, can provide data regarding inclinationrelative to the writing-surface area, and hence any related changes inwritten line width, and in parallax. A data stream generated from themonitoring structure which forms part of each transceiver structure inthe system can be used in a variety of ways, such as for example, tofeed information into the memory of a digital computer, and/or to feedinformation for transmission, for example over a voice-grade telephoneline, to remote stations for "live" presentation of "writing activity"occurring on the writing-surface area in the system, etc.

A modified form of the system utilizes a "nonmarking" stylus and a"nonerasing" eraser whose travel paths over the associatedwriting-surface area are followed to effect back-projection illuminationor de-illumination of a conventional translucent screen which forms thewriting-surface area.

The system of the invention employs conventional triangulation, derivedfrom the use of at least two, spaced transceiver-structure stations, totrack the position and motion of a writer or eraser, and the componentsof the system are readily retrofittable, at relatively low cost, to awide variety of otherwise conventional writing-surface structures, suchas so-called dry-erase whiteboards.

Various other features and advantages which are attained and offered bythe invention will become more fully apparent as the description whichnow follows is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation, in schematic form, illustrating, as will beexplained below, a preferred embodiment, and one modification, of agraphic data-acquisition system constructed in accordance with thepresent invention, all illustrated in connection with the drawing(writing) of a single line.

FIG. 2 is an enlarged, schematic detail of one of two transceiverstructures employed in the system of FIG. 1.

FIG. 3 is a schematic view taken generally along the line 3--3 in FIG.1.

FIG. 4 (second plate of drawings) is an enlarged, fragmentary detailillustrating a writing stylus, and use thereof, in the system of FIG. 1,with the long axis of the stylus shown disposed substantially normal tothe plane of a writing-surface area in the system.

FIG. 5 is similar to FIG. 4, except that it shows the writing stylusdisposed with its long axis at an angle α (in the plane of FIG. 5)relative to the plane of the writing-surface area.

FIG. 6 is an enlarged, fragmentary, schematic detail relating to FIGS. 4and 5, illustrating one form of a linear, light-reflecting bar code(code structure) on the writing implement depicted in FIGS. 4 and 5, andshowing, in relation thereto, pulse trains that are indicative of scanreflections received by a transceiver structure in the system inrelation to the two "writing angles" depicted in FIGS. 4 and 5.

FIG. 7 is a developed, schematic strip drawing illustrating a bar codelike that shown in FIG. 6.

FIGS. 8, 9 and 10 are somewhat like FIG. 7, and illustrate severaldifferent modifications of a bar code, or code structure, with FIGS. 8and 9 illustrating what are referred to herein as unilinearallydistributed codes, and with FIG. 10 illustrating what is referred toherein as a bilinearally distributed code.

FIG. 11 is an isometric view of a preferred form of a free-standingeraser, having a round erasure expanse, employed in the system of FIG.1.

FIG. 12 (third plate of drawings) is similar to FIG. 1, with theexception that it illustrates use of the eraser of FIG. 11 to create aswath over the writing-surface area in the system, which swath removesthe line created by the writing shown in the illustration of FIG. 1.

FIGS. 13, 14 and 15 (fragment only) illustrate isometrically threedifferent modifications of free-standing erasers employable in thesystem of the invention.

FIG. 16 (second plate of drawings) illustrates a modified form of roundor circular eraser which snaps removably onto that end of the writingstylus shown in FIGS. 4 and 5 which is remote from the "writing end".

DETAILED DESCRIPTION OF, AND BEST MODE FOR CARRYING OUT, THE INVENTION

Turning attention now to the drawings, and referring first of all toFIGS. 1-3, inclusive, indicated generally at 10 is a one-to-one, graphicdata-acquisition system constructed in accordance with a preferredembodiment of the present invention. System 10 is mounted and positionedfor use with respect to the writing-surface area 12a of an upright,otherwise conventional, dry-erase whiteboard which includes animplement-support ledge 12b on which rest two mobile, write-effectivecomponents, including a pen (stylus), or writing instrumentality, 14,and an eraser, or deleting or erasing instrumentality, 16, eachconstructed in accordance with the invention and provided as componentsin system 10. Further included in the system, and located at two, spacedstations adjacent the upper corners of board 12, are two, activetransceiver structures 18, 20 which are alike in construction, and whichare of conventional and readily commercially available design. As willbe explained, structure 18 functions to create, over and closelyadjacent writing-surface area 12a, a pattern of scanned opticalradiation that lies within and partially defines a scanning zone whichis partially bounded by dash-dot lines 18a, 18b. Scanning occurs bystructure 18 in successive, clockwise sweeps in the rotary direction ofarrow 22, and as will be explained, certain structure within transceiverstructure 18 responds to any return-response radiation that returns froma reflecting or retroreflecting object within the scan zone. In thisregard, I will later describe usable system modifications wherein"response" activity does not depend upon reflection or retroreflection.Structure 20 operates (independently) in a similar fashion to contributeto the mentioned scanning zone by creating a pattern of scanned lightlying between dash-dot lines 20a, 20b. The scanning rate associated withtransceiver structure 20 is the same as that associated with structure18, and the scan direction is also clockwise (as viewed in the FIG. 1)in the direction of arrow 24. The scan rate associated with each of thetwo transceiver structures herein is 1000-scans-per-second.

FIG. 2 illustrates the conventional make-up, for example, of transceiverstructure 18, and this structure is seen to include a laser 26, afocusing lens 28 which, in cooperation with the laser, creates a narrow,collimated beam, a dual-prism beam splitter 30, a lens 31, aphotodetector 32 and a faceted, polygonal, rotating mirror 34 which isdriven by a suitable, brushless, DC motor (not shown), and which rotatesabout axis 34a in the direction of previously mentioned arrow 22. Laser26, lens 28, beam splitter 30 and mirror 34 are referred to hereincollectively as scanning light-beam-source structure, or as activeoptical structure. Photodetector 32, lens 31, along with beam splitter30 and mirror 34, are referred to herein collectively as alight-reflection (or as light-retroreflection) monitoring structure, andalso as reaction monitoring structure.

Laser 26 operates at the wavelength indicated earlier, and produces abeam of light which passes through lens 28 and beam splitter 30 tostrike mirror 34 whose rotation causes this beam to scan in successive(1000-times-per-second) sweeps in parallel, closely spaced fashion overwriting-surface area 12a. In the preferred system embodiment now beingdescribed, any such light which is reflected from the scanning zoneadjacent the writing-surface area, back toward mirror 34, is notedinstantly by way of its striking beam splitter 30, and at leastpartially deflecting, as indicated, toward photodetector 32. Thephotodetector produces, on an output cable indicated generally at 32a, asignal which is directly related to the received, reflected radiation.

Transceiver structure 20 is substantially the same in construction andoperation as structure 18.

The highly simplified view which is presented in FIG. 3 illustrateswhiteboard 12 and writing-surface area 12a, with mirror 34 andtransceiver structure 18 shown at the left side of the figure, and witha mirror 36 which, in transceiver structure 20 is the counterpart tomirror 34, shown adjacent the right side of FIG. 3. Mirror 36 rotates inthe direction of previously mentioned arrow 24 about an axis 36a. Theoperations of these two mirrors with respect to their associated laserscreates the previously mentioned scanning zone, indicated now generallyat 38 in FIG. 3, which zone closely overlies (in a parallel manner)writing-surface area 12a. Zone 38 is bounded in system 10 by lines 18a,18b, 20a, 20b, and by ledge 12b.

Continuing with a description generally of what is included in system10, and returning attention specifically to FIG. 1, included in thesystem, preferably, is a digital signal processor, or interpretationstructure, 40 which receives, from transceiver structures 18, 20,signals relating to detected reflections. These signals are fed to theprocessor via previously mentioned cable 32a which extends fromtransceiver structure 18, and by a cable 42 which extends in likefashion from the companion photodetector (not shown) that forms part oftransceiver structure 20. Processor 40 is coupled to an output bus 44which can be used selectively and operatively as a "feed" connection toa remote terminal/viewing station, a telephone data-transmission line,etc.

Completing a general description of system 10, each of the twowrite-effective components - - - pen 14 and eraser 16 - - - is equippedpreferably with light-retroreflecting (reflecting) bar codes 46, 48,respectively, which are also referred to herein as optically reactive,selected-characteristic-identifying code structures.

Taking a look now specifically at FIGS. 4-7, inclusive (plate two in thedrawings), pen 14 herein includes an elongate cylindrical body having awriting-tip end 14a adjacent which is provided a writing tip 14b. Tip14b might have any selected shape, and herein is shown with a generallyrounded, conical shape which is capable, depending upon the angulardisposition employed for the pen during a writing operation, to create,on writing-surface area 12a, line widths which are different. In FIG. 4,pen 14 is shown in a writing condition with its long axis 14c disposedsubstantially normal to writing-surface area 12a. In this condition,writing motion of the pen over the writing-surface area creates a linehaving a nominal width indicated at T₁.

Code structure 46 herein takes the form of a band distributed around thebody of the pen adjacent end 14a, which band includes an organizedbar-code arrangement of longitudinally extending, differentiatedretroreflecting regions, such as "strong" retroreflecting regions 46a(see FIG. 6) interspersed with substantially non-retroreflectingregions, such as regions 46b. Regions 46a, 46b are distributedcircumferentially about pen 14 in what might be thought of as a lineardisposition (circumferentially speaking) with each of these regions,relative to axis 14c, subtending substantially the same angle. FIG. 7,which shows what might be thought of as a developed or laid out view ofa fragment of code structure 46, illustrates the "uniform angular width"nature of interspersed regions 46a, 46b. This, as should be appreciated,is but one of an infinite variety of angular-disposition patterns whichmay be chosen for a code structure.

Code structure 46 is positioned on pen 14 at a location whereby, withthe pen in the disposition shown for it in FIG. 4 relative towriting-surface area 12a, the code structure optically "intersects"scanning zone 38. In a broad sense, this interaction is also referred toherein as a field-electromagnetic engagement with zone 38. As depictedin FIG. 4, the bar regions in code structure 46, under thesecircumstances, substantially symmetrically "straddle" (in a verticalsense) the "plane" of scanning zone 38. The lengths of these bar regionsare chosen herein to create a situation whereby, under circumstanceswith pen 14 tilted at a selected, pre-planned writing inclination whichis the maximum expected writing inclination relative to writing-surfacearea 12a (see particularly angle α in FIG. 5), the bar regions willstill optically intersect the plane of scanning zone 38.

Deflecting attention for a moment to FIG. 5, and considering thesituation there illustrated with pen 14 tilted at angle α in the planeof FIG. 5 relative to writing-surface area 12a, two interesting mattersshould be noted. First, and because of the nature and configuration ofwriting tip 14b, the nominal line width which will be written by the penunder these circumstances is greater than that illustrated in FIG. 4,and is shown in FIG. 5 as T₂. Further, there is a lateral, verticalprojection-displacement on and along surface 12a between the writingextremity of tip 14b and the point of intersection of the plane of zone38 and axis 14c, and this displacement represents a parallax conditionwhich is indicated in FIG. 5 at P. More about these changed conditionswill be said shortly.

According to the invention, the code structure associated with pen 14 ischosen to be specific to that component. Herein, it specificallyidentifies the component as a writing pen, and further providesinformation about the writing "color" of the pen, and about thewriting-tip configuration or topography. The creation of such a specificcode for a given component is well within the skill of those havingknowledge in the art, and thus can readily be tailored (without anydetailed elaboration herein) to be unique for each given type ofwrite-effective component employed in the system of the invention. Forexample, FIGS. 8, 9 and 10 show three different kinds of code structureswhich are among the infinite variety available to the implementor of thesystem. FIG. 8 shows a linearally distributed bar code in whichretroreflecting and non-retroreflecting elongate bands are linearallydistributed, with the retroreflecting regions each subtending a likeangle relative to a supporting circumferential or cylindrical surface,and with each non-retroreflecting band subtending a like but smallerangle. FIG. 9 illustrates a linearally distributed bar code which ischaracterized by angular variance, in the sense that, as one progressesaround the supporting cylindrical surface, adjacent retroreflecting barregions subtend different angles, and the same is true with respect tointerleaved, non-retroreflecting bar regions. This kind of a code isparticularly useful in enabling the system to detect the rotationalangular position of a write-effective component over surface 12a, assuch component is viewed from the point of view of FIG. 1. FIG. 10illustrates a bilinearally (along two axes) distributed code structurein which patches of retroreflecting material are interleaved by ways andalleys of non-retroreflecting material. These illustrations, andstressing a point which has already been made herein, are but a very fewrepresentations of the differentiated ways in which code structures canbe constructed for use in the system of the present invention.

Returning attention to FIG. 1, along with several of the other figureswhich have already been discussed, FIG. 1 is employed also to illustratea typical single-line drawing operation, and in this context, pen 14a isshown in the figure as having been moved from position 14A along a wavyline 50 to a terminal position shown at 14B. Terminal points 14A, 14Bare indicated by dash-dot lines in FIG. 3, which lines also bear thedesignator 14c to indicate the location of the pen's longitudinal axis.Assuming that pen 14 is in the position relative to writing-surface area12a as shown in FIG. 4, line 50 has the width T₁ and code structure 46intersects scanning zone 38 as indicated in FIG. 4. In general terms,and as will now be more fully explained, with system 10 operating,movement of the pen in the fashion just described is noted bytransceiver structures 18, 20, whose photodetectors transmit toprocessor 40 signals in the form of pulses relating to retroreflectionactivity, which pulses are interpretable by the processor to track theposition and motion of the pen, as well as to identify the character,color and inclination of the pen.

Looking at FIG. 6, the body of pen 14 is here fragmentarily shownupright in the drawing relative to a horizontal surface 52 which can bethought of either as representing, or as being coincident with,writing-surface area 12a. Given the nature of the differentiatedretroreflecting bars or bar regions that make up code structure 46, andtheir dispositions relative to the plane of scanning zone 38 asillustrated in FIG. 6, each transceiver structure in the system receivesa retroreflection return which creates, on a time base, such as timebase t₀, a string of pulses like those shown at 54 in FIG. 6. Processor40 is equipped according to the invention, and by the utilization ofconventional techniques, with a look-up table structure which enables itto identify, from this string of pulses, the operative nature(character, angular disposition, color, etc.) of pen 14. "Tracking" ofthe pen by both transceiver structures, an operation performed on therespective output signals by processor 40, to effect conventionaltriangulation procedures, enables the processor to "know" preciselywhere writing is occurring with motion of the pen. Thus, under thecircumstances now being described, a data stream will be created on bus44, which stream can be employed for feeding to remote stations, etc.,to reflect accurately the drawing of line 50, with appropriate color andline width.

Had line 50 been created with pen 14 oriented nominally at an angle suchas angle α (see FIG. 5) to the plane of writing-surface 12a, each of thetwo transceiver structures would receive a retroreflection responsedifferent from the other transceiver structure and different from theresponse which produced the chain of pulses illustrated at 54 in FIG. 6.For example, one such different chain of pulses 56 is illustrated alonga time base t.sub.α extending at an angle α relative to line 52 in FIG.6. With regard to this activity, the output signals from the transceiverstructures are processed by processor 40, in the sense of their beingcompared to the look-up table structure provided, from which theprocessor can develop an output data stream which now reflects thechanged line width that has been drawn, as well as the issue of parallax(so that a remote station will be capable of recreating precisely thelocation and disposition of line 50).

The look-up table structure provided for the processor can beconstructed to have any desired degree of "resolution" such that, forexample, different "writing angles" within different subranges of anoverall permissible maximum writing angle α, in relation to thelocations of the transceiver structures, are available for accuratedetermination of written-information location. As was mentioned, thecreation of such tables is well within the skill of those experienced inthis field of art.

Directing attention now to FIGS. 11 and 12, FIG. 11 illustrates thepreferred form of eraser 16 which includes a circular body 16a, amanipulation handle 16b which is joined to the top surface of body 16a,and a round, or circular, eraser pad expanse 16c joined to the undersideof body 16a. Code structure 48 is a linearally distributed bar codehaving differentiated retroreflecting and non-retroreflecting bands(like those previously mentioned) formed on the perimeter of body 16a asshown. Processor 40 is equipped, in its look-up table structure, withinformation that specifically relates to code structure 48 vis-a-visidentifying that component 16 is an erasing instrumentality, and furtheridentifying that it is circular in nature and that it has a certaindiameter D₁ (see FIG. 12). Given this, and looking at a situationillustrated in FIG. 12, here, eraser 16 is illustrated as having beenmoved to create an eraser swath directly overlying, and thus removing,previously mentioned drawn line 50, with the eraser moving from astarting position 16A to an ending position at 16B. Transceiverstructures 18, 20 track this activity and provide signals to processor40 which signals indicate precisely what has occurred so that theprocessor can provide, via bus 44, a data stream which effects "erasure"of line 40 from the remote displays, or the like.

FIG. 13 illustrates a modified form of eraser 58 which includes anoblong, rectangular body 58a, a cylindrical riser 58b whose perimetercarries a code structure 60, a manipulation handle 58c which is joinedto riser 58b, and an oblong, rectangular erasure pad 58d that fits onthe bottom of body 58a. Code structure 60 is constructed to have anappropriate angular variance, such as that illustrated in FIG. 9, sothat the angular, rotational disposition of eraser 58, relative to theplane of writing-surface area 12a, can be determined, thus to indicatethe nature (width) in real time of the erasure swath which is created bymotion of eraser 58 over the writing-surface area.

FIG. 14 illustrates yet another modified form of a free-standing eraser.Here there is shown at 62 an eraser which includes a hollow, oblong,rectangular body 62a whose side walls are formed of a suitable plasticmaterial which is substantially transparent to the wavelength ofradiation employed by transceiver structures 18, 20, and within which islocated a cylindrical structure 62b whose perimeter carries a codestructure 64 which is like previously mentioned code structure 60.Through the walls of the body, code structure 64 is able optically tointeract with radiation in zone 38. Joined to body 62a is a manipulationhandle 62c.

FIG. 15 illustrates, very fragmentarily, yet another modified form offree-standing, oblong, rectangular eraser, similar in some respects toerasers 58, 62, wherein the four corners of the body are "clipped" asillustrated at 65 to carry strips of code structure, such as the codestructure illustrated at 66 in FIG. 15. 10 With this kind of anarrangement, and with appropriate look-up table structure, processor 40can determine not only the rotational position, relative towriting-surface area 12a, of an eraser so constructed, but also can tellwhether such an eraser is tilted away from area 12a so that it is beingheld to erase, not across the broad expanse of its erasure pad, butrather along one of the linear edges of this expanse.

Moving along in this description, FIG. 16 (second plate of drawings)illustrates at 68 a small cylindrical eraser which is adapted to besnap-fitted onto the non-writing-tip end of the body of pen 14. Thiseraser includes a small circular erasure pad 68a having a diameter D₂which is considerably smaller than the diameter D₁ of eraser 16. Eraser68, on its cylindrical body 68b, carries a linear, retroreflectingbar-code structure 70. While this structure has been described herein asone that snap-fits onto the body of pen 14, it is possible of coursethat the pen can be constructed with such an eraser permanently inplace.

In all of the descriptions so far, the system has been described in thecontext of one wherein a pen, such as pen 14, produces an actual mark ona writing-surface area, such as on writing-surface area 12a, and whereinan eraser, such as eraser 16, removes an actual mark. A modification canreadily take the form of a system wherein the writing-surface areaactually forms the front face of a translucent projection screen, withrespect to which there is provided conventional back-projectionequipment that responds to a data stream on bus 44 to project, orde-project, in real time, a light image which creates a virtual writingor drawing in response to motion of a "writing" and/or "erasing"component adjacent the writing-surface area. In FIG. 1, indash-double-dot lines at 72, such a back-projection system is showncoupled through a data bus 44a to processor 40. FIG. 12 includes, indash-double-dot lines, an illustration of the same modified system(performing during an erasure operation).

Accordingly, a unique graphic data-acquisition system, based on the useof implement-specific code structure which is passive on awrite-effective component, has been disclosed. This system will be seento offer all of the features and advantages that are made available inthe various prior art systems mentioned earlier, and in addition tooffer a number of new and important operational and characteristicadvantages.

The preferred forms of the system have been described in conjunctionwith the use, on the so-called write-effective components, of a codestructure which is formed from differentiated retroreflecting regions.Retroreflective structure could, if desired, be replaced bynon-retroreflective, but nevertheless appropriately, generallyreflective material. In a very simple application, the code structurecould take the form of a single bar or band of reflecting material. Inaddition, other kinds of passive, scanning-reactive code structurescould be used. For example, radiation scanned from the transceiverstructures could be employed to excite a coded pattern of phosphorcarried on a component, excitation of which phosphor could be picked upby appropriate photodetectors. In this case, such excitation would notproperly be referred to as reflection activity, but rather morecorrectly as radiation-responsive activity. Another possibility is thatradiation from the transceiver structures could excite a material whichresponds to the stimulating wavelength by emissions of a different onethat could be picked up by suitable detectors. Still a furtherpossibility is that transceiver radiation could excite a code materialwhich responds by heating to some extent, and whose radiated/heatedcondition could be picked up by suitable infrared detectors. Otherpassive code-structure possibilities may be usable as well.

It is desired to secure and claim by Letters Patent:
 1. A writing pathtracking system comprising:a flat board having an erasable writingsurface; a writing implement including a pigment supply in communicationwith a tip capable of contact-initiated removable pigment deposit on thewriting surface, and a light reflective, character-indicative, codepattern disposed on a surface of the implement; a scanninglight-beam-source disposed adjacent the writing surface and operable togenerate a defined pattern of scanned light in a scanning zone, spacedclosely and generally parallel to the writing surface so that the codepattern of the implement is located in the scanning zone when the tip ofthe implement is contacting the writing surface; light-reflectionmonitoring structure positioned adjacent the writing surface and capableof receiving light reflectance signals from the code pattern andconverting the signals into an analog data stream indicative ofimplement position and character; a processor communicatively connectedto the monitoring structure and capable of receiving, digitizing andinterpreting the data stream, then displaying at a location remote fromthe board, an image-reproduction corresponding to an actual writtenimage on the board.
 2. The system of claim 1 wherein the scanninglight-beam-source includes at least a first laser scanner and a secondlaser scanner, each scanner being spaced apart from the other scanneraround a peripheral region of the writing surface.
 3. The system ofclaim 1 wherein the code pattern indicates one of the followingqualities of the implement: pigment color, line width, inclinationrelative to the writing surface.
 4. The system of claim 1 wherein thecode pattern is a bar code disposed around a circumferential surface ofthe implement.
 5. The system of claim 1 wherein the board is a dry-erasewhiteboard.
 6. The system of claim 1 further comprisinga plurality ofwriting implements, each implement carrying a supply of pigment forcontact-initiated deposit on the writing surface, and having adifferentiating reflective code pattern denoting a characteristic of thepigment.
 7. The system of claim 6 wherein the characteristic of thepigment is color.
 8. A writing implement comprising;an elongate bodyhaving a peripheral surface near a writing tip, and containing a pigmentsupply accessible to the writing tip; a code pattern disposed on theperipheral surface of the body, wherein the code pattern indicates atleast one characteristic of either the pigment or the writing tip; andwherein the code pattern is circumferentially constant so that the codepattern can be interpreted by a scanner-monitoring device to provide thesame characteristic information regardless of which side of theimplement is exposed to the scanner-monitoring device.
 9. The writingimplement of claim 8 wherein the code pattern indicates the color of thepigment.
 10. The writing implement of claim 8 wherein the code patternindicates at least one geometrical feature of the writing tip.
 11. Aplurality of writing implements, each implement according to claim 8,wherein its code structure differentiates it from the other implements.